1. Field of the Invention
The present invention relates to a lithographic apparatus and a method for manufacturing a device.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In the known lithographic apparatus, a patterning device exchange device is used to exchange patterning devices between a stationary patterning device station, such as a loading station, inspection station, cleaning station or library and the patterning device support on which a patterning device is supported during projection of the pattern of that patterning device on a substrate. The known patterning device exchange device includes a robot having one loading position and a turret having two holding positions. The robot is configured to exchange a patterning device between a loading station and one of the holding positions of the turret and vice versa. The turret is configured to exchange a patterning device with the patterning device support. The time needed to exchange a patterning device on the patterning device support takes at least the time to lift the patterning device on the patterning device support out of the pod hole wherein it is supported during the projection phase so that the turret can take over the patterning device from the patterning device support. Thereafter the turret has to rotate over 180 degrees so that a new patterning device which was already present in the other holding position of the turret is brought in a position wherein it can be exchanged with the patterning device support. Then, the new patterning device is placed on the lifting pins of the patterning device support and lowered into the pod hole. When the patterning device is positioned in the pod hole the patterning device support can be moved back to a position above the lens column and the projection phase can begin.
The exchange of a patterning device in the known lithographic apparatus may take a considerably long time. This long exchange time is of direct influence on the throughput performance of the lithographic apparatus.
It has been proposed to use turrets having more than two holding positions in order to make a quicker exchange of patterning devices possible. Also, other embodiments of the patterning device exchange device have been proposed to decrease the time needed. However none of the alternative embodiments of the patterning device exchange device have been proven to substantially lower the exchange time needed to exchange a patterning device to a satisfactory level.
Furthermore, new projection techniques, such as stitching with four or more patterning devices or multiple (double) exposure, which require more different patterning devices of which the pattern has to be projected quickly after each other make the requirement of smaller exchange times of a patterning device even more important with respect to the increasing of the throughput performance of the lithographic apparatus.